This study aims at the synthesis of silver and copper oxide nanoparticles and the preparation of highly concentrated suspensions thereof for their use as printable conductive inks, suitable for printing techniques with high viscosity and nanoparticle concentration requirements, for the fabrication of electronics. The synthesis was carried out in glycol-water co-solvent media under microwave irradiation, which increased the reaction yield and rate, led to the formation of homogeneous nanoparticles of narrow size distribution and enabled size and shape control. The particles were coated by a protein capping agent. UV-Visible Spectroscopy and Scanning Electron Microscopy (SEM) confirmed the formation of nanoparticles. Attenuated Total Reflectance - Fourier Transform Infrared (ATR-FTIR) provided information about reactions of the organic species present in the reaction mixture. The synthesis reaction yield was studied via X-ray Photoelectron Spectroscopy (XPS). Next the concentration and viscosity of the synthesized suspensions were regulated according to the specifications of the printing technologies. Particle concentrations varied from 20 to 60 wt.% and the viscosity of the final suspensions was greater than 10,000 cP. The concentration was confirmed via Thermogravimetric Analysis (TGA) and the viscosity was determined via rheological measurements. The inks prepared were stable in the course of a few months, as was confirmed via UV-Visible Spectroscopy. SEM and Transmission Electron Microscopy (TEM) revealed particles smaller than 100 nm, with unimodal size distribution. The research work was supported by the Hellenic Foundation for Research and Innovation (HFRI) under the 3rd Call for HFRI PhD Fellowships (Fellowship Number: 5238).